NBN is expected to be fully rolled out by 2020. ()The project has cost Australian taxpayers billions of dollars. ()

It was also admitted the network is not commercially viable as retailers decline to purchase sufficient bandwidth while aggressively competing against each other for new customers who aren't prepared to pay more for faster broadband services.

The NBN is trialling fibre-to-the-curb technology, which takes cable to telecom pits outside premises, which is closer than fibre-to-the-node as well as cheaper and less complex than fibre-to-the-premises.

NBN Co expects to serve an initial one million premises with FTTC and estimates the technology will cost about $2900 per premises to deliver compared to $4400 for FTTP.

The Telecommunications Industry Ombudsman's annual report released last week showed NBN complaints, including those about delayed connections, soared from 10,487 to 27,195.